1. Filed of the Invention
The present invention relates to a method for preparing a polymer by anionic polymerization of a polar unsaturated compound. The polymer or copolymer is a very important polymer for use as a raw material of a polymeric material or a functional polymer.
2. Description of the Related Art
A great number of studies have been made on anionic polymerization of a polar unsaturated compound for a long period of time and various technique have hitherto been developed (e.g. xe2x80x9cLectures: Theory of Polymerization Reaction, IV Anionic Polymerizationxe2x80x9d, issued by Teiji TSURUTA, page 12, Kagaku Dojin (1973); and New Polymer Experimental Science, Vol. 2, xe2x80x9cSynthesis and Reaction of New Polymer (1), Synthesis of Addition Polymerxe2x80x9d, pages 165 to 196, Kyoritsu Shuppan Co., Ltd. (1995)).
It has been well known that metal-containing catalysts, for example, metals such as alkali metal or alkali earth metal or a compound thereof, typical metallic complex, rare earth metal complex, etc. cause anionic polymerization (nucleophilic polymerization) of the polar unsaturated compound.
However, various physical properties and thermal stability of the polymer obtained by using the metal-containing catalyst are drastically influenced by remained metallic components, thereby requiring a special method or complicated step of sufficiently removing these metallic components in the preparation of the polymer.
It has also been publicly known that metal-free catalysts, for example, amine compounds, quaternary ammonium salts, quaternary phosphonium salts, etc. cause anionic polymerization. However, the amine compounds have a problem that the polymerization activity is poor and odor of the amine component is remained in the obrained polymer, whereas, the quaternary ammonium salts and quaternary phosphonium salts have a problem that they must be stored at a low temperature because of poor stability and the catalyst is decomposed during the polymerization reaction.
There has also been known an example wherein methyl methacrylate was polymerized in the presence of a phosphazene compound as a non-metallic catalyst (T. Pietzonka, D. Seebach, Angew. Chem. Int. Ed. Engl. 1993, 35, 716). Although the phospazene compound used in this method is an effective catalyst having strong basicity, a complicated step is required to synthesize the phosphazene compound and, moreover, a stronger basic compound such as potassium amide must be used to impart strong basicity (Nachr. Chem. Lab. 1990, 38, 1216). Therefore, the phosphazene compound is not advantageous from an industrial point of view. Also the compound has poor handling, that is, properties are liable to be changed by a carbon dioxide gas in an air because of its strong basicity.
It has been found that poly(methyl methacrylate) obtained by polymerizing methyl methacrylate using the phosphazene compound with reference to the above documents is a mixture of a two kinds of polymers whose number-average molecular weight are 64,400 and 8,800 as shown in Comparative Example 1. As shown in Comparative Example 2, poly(methacrylonitrile) obtained by polymerizing methacrylonitrile was also a mixture of two kinds of polymers. These results show that the polymerization reaction using the phosphazene compound as the catalyst is not accurately controlled.
An object of the present invention is to find a catalyst which is easily prepared and does not require any care about a storing process or decomposition during the polymerization in anionic polymerization of a polar unsaturated compound, and which does not contain any metallic component and has high activity, and which does not remain odor in the obtained polymer and is superior in ability of controlling the polymerization reaction, and to provide a method of efficiently preparing a polymer by using the catalyst.
To attain the above object, the present inventors have intensively studied. As a result, we have found a phosphazenium compound represented by the formula (1) is a remarkably effective catalyst which does not require any care about a storing process or decomposition during the polymerization and exhibits a high catalytic activity to anionic polymerization of a polar unsaturated compound, whereby the polymerization reaction proceeds while maintaining a living polymer regardless of the presence or absence of an active hydrogen compound, and not only an average molecular weight but also the number of moles of the resulting polymer can be controlled. Thus, the present invention has been completed.
That is, the present invention provides a method for preparing a polymer, which comprises subjecting a monomer containing at least a polar unsaturated compound to anionic polymerization in the presence of a phosphazenium compound represented by the formula (1): 
(wherein Zxe2x88x92 is an anion of an active hydrogen compound in the form where a proton is eliminated from the active hydrogen compound and transferred to the anion; a, b, c and d each represents 1 or 0, but all of them are not simultaneously 0; and R may be the same or different and each represents a hydrocarbon group having 1 to 10 carbon atoms, and two R(s) on the same nitrogen atom are optionally combined each other to form a cyclic structure), or in the presence of the phosphazenium compound and the active hydrogen compound.